JP3280844B2 - Method for forming insulating film on unidirectional silicon steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the and forsterite (Mg ₂ SiO ₄₎ oriented silicon steel sheet inorganic mineral coating intentionally prevented to finish annealing already produced a generation of such, once generated folder The inorganic mineral film such as stellite is removed by means of pickling or the like, and furthermore, a good iron loss can be obtained for the finish-annealed unidirectional silicon steel sheet prepared to a mirror surface or a state close thereto. Another object of the present invention is to provide a method for forming a tension imparting type insulating film having excellent film adhesion.

[0002]

2. Description of the Related Art A grain-oriented silicon steel sheet is widely used as a magnetic iron core material. In particular, a material having a small iron loss is required to reduce energy loss. It is effective to apply tension to the steel sheet to reduce iron loss, so by forming a film made of a material having a smaller coefficient of thermal expansion at a high temperature compared to the steel sheet, tension is applied to the steel sheet to reduce iron loss. It has been planned. The forsterite-based coating formed by the reaction between the oxide on the steel sheet surface and the annealing separator in the finish annealing step can give tension to the steel sheet and has excellent coating adhesion.

Furthermore, the method of forming an insulating film by baking a coating solution mainly composed of colloidal silica and phosphate disclosed in Japanese Patent Application Laid-Open No. 48-39338 has a large effect of imparting tension to a steel sheet. It is effective for reducing iron loss. Therefore, it is a general method for manufacturing a unidirectional silicon steel sheet to form an insulating film mainly composed of silica and phosphate while leaving the forsterite-based film generated in the finish annealing step.

On the other hand, in recent years, it has become clear that the disordered interface structure between the forsterite-based coating and the ground iron has reduced the iron loss improving effect to some extent due to the coating tension.
Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 49-96920, by removing a forsterite-based film generated in the finish annealing step, or performing a mirror finish, and then forming a tension film again. Technology to further reduce iron loss has been developed.

[0005] However, when the above-mentioned insulating film is formed on a film mainly composed of forsterite, a considerable film adhesion can be obtained, but the forsterite-based film is removed or intentionally used in the finish annealing step. The film adhesion is not sufficient for the one without forsterite formation. When the forsterite-based film is removed, it is necessary to secure the required film tension only with the tension-providing insulating film formed by applying the coating liquid, and the film must be thickened inevitably. Is required. Therefore, it is difficult for the conventional film forming method to achieve a film tension sufficient to bring out the effect of mirror finishing, and a sufficient reduction in iron loss has not been achieved.

Therefore, prior to applying a coating liquid for forming an insulating film, an SiO ₂ film is formed on the surface of the steel sheet (Japanese Patent Application Laid-Open No. 60-131976, Japanese Patent Application Laid-Open No.
184762) or annealing in a reducing atmosphere (Japanese Patent Application Laid-open No. 64-83619), and furthermore, phosphates and silicates (Japanese Patent Application Laid-Open No. 5-27974) or amorphous oxides (Japanese Patent Application Laid-Open No. No. 278833), a method has been proposed in which the adhesion of the insulating film is ensured by forming a base film, and the iron loss is reduced by the film tension.

[0007]

According to the above-described method, the film adhesion and iron loss can be improved and improved to some extent. However, there is no underlying treatment such as oxidation or reduction prior to the application of the coating liquid in the current production process of a unidirectional silicon steel sheet. Therefore, when these base treatments are to be performed on a finish-annealed unidirectional silicon steel sheet having no inorganic mineral matter film, new equipment installation and a new manufacturing process are required. As a result, there has been a problem that the cost has been significantly increased and it is difficult to implement industrially.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a tension-imparting insulating coating for a finish-annealed unidirectional silicon steel sheet without an inorganic mineral coating without increasing the cost. Is formed with good adhesion. The gist of the present invention is to apply a coating solution containing phosphate and colloidal silica as a main component to a finish-annealed unidirectional silicon steel sheet having no inorganic mineral substance film on the steel sheet surface, and baking the applied coating liquid. In the method of forming a film, the solid content ratio of silica to phosphate is set to 0.1.
This is a method for forming an insulating film on a grain-oriented silicon steel sheet having a thickness of 8 or more and 3.0 or less. In addition to the above-mentioned ratio, the coating amount per side of a coating solution for forming a tension-imparting insulating film is 1.0 g / side. The present invention relates to a method for forming an insulating film on a unidirectional silicon steel sheet having a thickness of not less than m ^{2 and not} more than 10.0 g / m ² .

The details of the present invention will be described below. The present inventors considered and considered whether a base treatment for securing the adhesion of a tension-imparting type insulating film, in particular, formation of a base oxide layer could be realized during baking of a coating liquid. In this case, in order for the steel sheet to be oxidized to form a base oxide layer, the coating must be permeable and an oxidizing gas can penetrate to some extent. However, a film having a conventional composition (weight ratio of solid content of silica to phosphate: about 0.7) is basically amorphous and has substantially no grain boundaries capable of expressing permeability. In addition, the surface morphology is extremely flat, and so-called cracks, cracks, and the like hardly exist. For this reason, the base composition cannot be formed because the film permeability is poor with the conventional composition.

In the first place, a tension-imparting insulating film mainly composed of phosphate and silica exhibits its tension-imparting property by silica having a small thermal expansion coefficient, but it is difficult for silica alone to form a film. Therefore, phosphate functions as a so-called binder component for fixing silica. By reducing the fraction of phosphate as a binder, the inventors introduced fine cracks in the film, adjusted the permeability of the film, and appropriately oxidized the steel sheet during baking of the coating solution. It was expected that a base oxide layer could be formed by this.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Based on this concept, the relationship between the solid content weight ratio of a film and the film adhesion was examined by conducting the following experiment. First, the forsterite-based film formed on the surface of the 0.23 mm-thick annealed unidirectional silicon steel sheet was removed by pickling, and the surface was mirror-polished by chemical polishing. Next, for this steel sheet,
Various coating solutions having different ratios of phosphate and colloidal silica were applied and baked at 835 ° C. for 30 seconds to form a tension-imparting insulating film. Finally, the film adhesion of the sample with the film was measured by a cylinder bending test (the sample was wound around a cylinder having a diameter of 20 mm, and the state of film peeling on the inner surface side was visually determined). Table 1 shows the results.

[0012]

[Table 1]

From Table 1, it can be seen that the higher the solids weight ratio of silica to phosphate, the better the film adhesion, and particularly good when the ratio is 0.8 or more. You can see that. Here, the higher the solid content weight ratio of silica to phosphate, the higher the degree of crack introduction. However, if the ratio is more than 3.0, cracks are excessively introduced and the film adhesion of the unidirectional silicon steel sheet as a film property. Since the required insulating properties and rust resistance are deteriorated in addition to the properties, the weight ratio of the solid content of silica to the phosphate must be 3.0 or less.

Thus, even for a grain-oriented silicon steel sheet without an inorganic mineral substance coating, new equipment and processes can be provided by setting the solid content weight ratio of silica to phosphate to be 0.8 or more and 3.0 or less. An insulating film can be formed with good adhesion without need. Next, the inventors examined the effect of the coating amount on the iron loss value.
In the case of No. 2, the relationship between the coating amount and the iron loss value was examined. First, with respect to a 0.23 mm-thick finish-annealed unidirectional silicon steel sheet, the forsterite-based coating formed on the surface was removed by pickling, and the surface was mirror-finished by chemical polishing. Next, for this steel sheet,
A coating solution having a ratio of various phosphates and colloidal silica of 1.0 is applied and baked at 835 ° C. for 30 seconds.
A tension-imparting insulating film was formed. Finally, the iron loss value was measured. For the measurement of the iron loss value, a magnetic domain control process is performed by a laser irradiation method, and the magnetic flux density (represented by B8) is 1.
The test was performed on samples around 94 Tesla. Generally, the iron loss value of a unidirectional silicon steel sheet is affected by the size of the magnetic domain and the magnetic flux density of the sample. For this reason, magnetic domain control was performed to equalize the sizes of the magnetic domains, and samples having substantially the same value of the magnetic flux density were selected, and the iron loss values were measured and compared. Thereby, it is possible to extract only the influence of the application amount on the iron loss value. Table 2 shows the results.

[0015]

[Table 2]

[0016] When 2 10G～m of ² or less coating weight per side 1 g / m ² or more from the table, is excellent iron loss value. Table 2 shows that the amount of coating affects the iron loss value, but the action is considered as follows. First, when the coating amount is less than 1 g / m ² per side, the absolute amount of the coating on the steel sheet is small, and the effect of reducing iron loss is hardly exhibited because the tension imparting property is not sufficient. On the other hand, if the coating amount is more than 10 g / m ² per side, cracks are excessively introduced, so that the base oxide layer is excessively developed, the mirror surface state is impaired, and the effect of reducing iron loss by the mirror surface is lost. .

As for the phosphate, two or more phosphates may be used in combination if the weight ratio of solid content to silica is adjusted. Further, even if chromic acid is added to the coating liquid in addition to phosphate and colloidal silica to improve rust resistance, the function and effect of the present invention are not impaired.

[0018]

EXAMPLES Next, examples will be described, but the present invention is not limited to these examples. Example 1 Decarburizing annealing was performed on a silicon steel sheet cold-rolled to a final thickness of 0.23 mm containing 3.25% of Si. At this time, an oxide layer containing SiO ₂ is formed on the surface of the steel sheet.
Next, an annealing separator mainly composed of MgO was applied to the steel sheet, and final finishing annealing was performed. A coating mainly composed of forsterite exists on the surface of the annealed silicon steel sheet thus annealed. The steel plate with the forsterite coating is immersed in an aqueous solution of sulfuric acid and ammonium fluoride to remove the forsterite coating, and then chemically polished in a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide to finish the surface to a mirror finish. Was.

Next, 110 ml of a suspension of colloidal silica having a concentration of 30% and a specific gravity of 1.21 was applied to the surface of the steel sheet at a concentration of 4%.
A coating solution (solid content weight ratio: 1.21: the present invention) consisting of 50% of a 4% aluminum phosphate solution having a specific gravity of 1.51 and 60 ml of a suspension of colloidal silica having a concentration of 30% and a specific gravity of 1.21 having a concentration of 44. %, A coating liquid consisting of 50 ml of an aluminum phosphate solution having a specific gravity of 1.51 (solids weight ratio: 0.66: comparative example) was applied at 4 g / m ² per one side by a grooved roll, nitrogen was 100%, and dew point was 30 ° C.
Baking at 835 ° C. for 30 seconds in an atmosphere of the above, a film was formed. Finally, the magnetic domain was controlled by a laser irradiation method.
Iron loss and film adhesion were measured. Table 3 shows the results.

[0020]

[Table 3]

Compared with the comparative example having a solid content weight ratio of 0.66, the present invention having a solid content weight ratio of 1.21 is superior in both iron loss value and film adhesion.

[0022]

As described above, according to the present invention, it is possible to form an insulating film having good film adhesion and excellent tension imparting property without increasing the cost without increasing the cost, and a low (excellent) iron loss value. Can be produced.

────────────────────────────────────────────────── ─── Continued on the front page (72) Ikuo Miyamoto 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (72) Inventor Osamu Tanaka Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka No. 46 at Nippon Steel Plant Design Co., Ltd. (56) References JP-A-5-311353 (JP, A) JP-A-5-287546 (JP, A) JP-A-6-184762 (JP, A) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 22/00-22/86 H01F 1/16

Claims (2)

(57) [Claims] 1. A tension-imparting insulating film formed by applying and baking a coating solution containing phosphate and colloidal silica as main components to a finish-annealed unidirectional silicon steel sheet having no inorganic mineral substance film on the surface of the steel sheet. , Wherein the weight ratio of solid content of silica to phosphate is 0.8 or more and 3.0 or less. 2. The coating amount per one side of a coating liquid for forming a tension imparting type insulating film is 1.0 g / m ² or more and 10.0 g / m ² or less.
3. The method for forming an insulating film according to item 1.